Nowadays, in the field of industrial gas turbines, a thermal barrier coating is capable of reducing the temperature of the heat-resistant alloy substrate of a turbine member such as a moving blade or stationary blade without altering the shape or cooling structure of the member, and therefore the use of such thermal barrier coating has become an essential technique.
The thermal barrier coating generally has a 2-layer structure in which a metal bonding layer formed from a MCrAlY alloy (wherein M represents Ni, Co, Fe, or an alloy thereof) with excellent oxidation resistance, and a ceramic layer with low thermal conductivity formed mainly from a zirconia-based ceramic are stacked sequentially on a heat-resistant alloy substrate.
One problem with these thermal barrier coating is that, for example, when a gas turbine is used for a long period of time at a high temperature exceeding 1500° C., a thermally grown oxide is generated on the metal bonding layer. As thermally grown oxide grows, it causes stress within the ceramic layer, which can cause cracking or peeling of the ceramic layer. Accordingly, the oxidation resistance of the metal bonding layer must be increased to suppress the growth rate of this thermally grown oxide.
Further, the temperature variations accompanying the starting and stopping of a turbine also cause thermal stress within the turbine member. As a result, cracks may occur in the metal bonding layer during operation of the turbine. Accordingly, the ductility of the metal bonding layer must also be improved.
CoNiCrAlY (Co-32Ni-21Cr-8Al-0.5Y) alloy is widely used as a material for the metal bonding layer, and although this alloy is capable of withstanding use within a 1500° C. class gas turbine, the oxidation resistance and ductility are inadequate for application to recently developed 1700° C. class ultra high temperature gas turbines. Consequently, significant effort is being devoted to developing alloys that are capable of withstanding ultra high temperatures. For example, PTL 1 and PTL 2 disclose alloy materials having high-temperature corrosion resistance that exhibit improved levels of oxidation resistance and ductility.
{Patent Literature}
    {PTL 1} Japanese Unexamined Patent Application, Publication No. 2003-183752    {PTL 2} Japanese Unexamined Patent Application, Publication No. 2003-183754